NASA Administrator Charlie Bolden has declared the James Webb Space Telescope (JWST) will not launch until at least 2018.
Bolden made the remarks on 11 April before a Congressional panel in Washington, DC.
The revised launch date is the latest in a series of blows to the troubled telescope programme, which is at least $1.5 billion over budget and four years behind the initially projected launch date.
In his Congressional testimony, Bolden said he would not ask for additional funds for the programme for fiscal year 2011. The agency does not believe it needs funding in the current fiscal year to allow it to continue to carry the JWST programme for "what we think now is a reasonable launch date of 2018", Bolden says.
NASA's FY2011 budget is contained within the continuing resolution authorising governmental expenditures, which the US Congress is due to vote on later today. It is widely anticipated that NASA will be authorised to spend slightly less than its FY2010 budget.
NASA's FY2012 budget requested $373 million for JWST, but Bolden notes that figure was preliminary. He aims to firm up NASA's request for FY2012 by May.
The Casani Report, an independent review of the JWST programme's budget and management released in November, suggested the launch would be delayed to recover from serious budgetary and management problems. The report stated that an additional $500 million would be required to launch at the earliest possible moment, anticipated to be September 2015. The rationale behind the 2018 date was not explained before Congressional committee.
The JWST is designed to measure infrared light, and is widely considered the successor to the iconic Hubble Space Telescope.